As is well known, the heart has four chambers for receiving and pumping blood to various parts of the body. During normal operation of the heart, oxygen-poor blood returning from the body enters the right atrium. The right atrium fills with blood and eventually contracts to expel the blood through the tricuspid valve to the right ventricle. Contraction of the right ventricle ejects the blood in a pulse-like manner into the pulmonary artery and each lung. The oxygenated blood leaves the lungs through the pulmonary veins and fills the left atrium. The left atrium fills with blood and eventually contracts to expel the blood through the mitral valve to the left ventricle. Contraction of the left ventricle forces blood through the aorta to eventually deliver the oxygenated blood to the rest of the body.
Myocardial infarction (i.e., heart attack) can result in congestive heart failure. Congestive heart failure is a condition wherein the heart can not pump enough blood. When patients have a heart attack, part of the circulation to the heart wall muscle is lost usually due to a blood clot which dislodges from a larger artery and obstructs a coronary artery. If the clot is not dissolved within about 3 to 4 hours, the muscle which lost its blood supply necroses and subsequently becomes a scar. The scarred muscle is not contractile, and therefore it does not contribute to the pumping ability of the heart. In addition, the scarred muscle is elastic (i.e., floppy) which further reduces the efficiency of the heart because a portion of the force created by the remaining healthy muscle bulges out the scarred tissue (i.e., ventricular aneurism) instead of pumping the blood out of the heart.
Congestive heart failure is generally treated with lots of rest, a low-salt diet, and medications such as A.C.E. inhibitors, digitalis, vasodilators and diuretics. In some myocardial infarction instances, the scarred muscle is cut out of the heart and the remaining portions of the heart are sutured (i.e., aneurismechtomy). In limited circumstances a heart transplant may be performed. The condition is always progressive and eventually results in patient death.
Collagen-containing tissue is ubiquitous in normal human body tissues. Collagen makes up a substantial portion of scar tissue, including cardiac scar tissue resulting from healing after a heart attack. Collagen demonstrates several unique characteristics not found in other tissues. Intermolecular cross links provide collagen-containing tissue with unique physical properties of high tensile strength and substantial elasticity. A property of collagen is that collagen fibers shorten when heated. This molecular response to temperature elevation is believed to be the result of rupture of the collagen stabilizing cross links and immediate contraction of the collagen fibers to about one-third of their original length. If heated to approximately 70 degrees Centigrade, the cross links will again form at the new dimension. If the collagen is heated above about 85 degrees Centigrade, the fibers will still shorten, but crosslinking will not occur, resulting in denaturation. The denatured collagen is quite expansile and relatively inelastic. In living tissue, denatured collagen is replaced by fibroblasts with organized fibers of collagen than can again be treated if necessary. Another property of collagen is that the caliber of the individual fibers increases greatly, over four fold, without changing the structural integrity of the connective tissue.
U.S. Pat. No. 6,071,303 teaches a device and method for treating infarct scar tissue of a mammalian heart by selectively heating the infarct scar to reduce the size of the scar tissue surface area, increase the cross-section of the scar tissue, stiffen the floppy portion of the scar tissue, reduce the ventricular systolic wall tension, and increase the overall pumping efficiency of the infarcted heart by eliminating the ventricular aneurism or dilated ventricle, if present. FIG. 1 illustrates an embodiment of the device taught in U.S. Pat. No. 6,071,303.
Referring to FIG. 1, there is illustrated a heart 10 having an infarcted region or portion 12. The infarcted portion 12 of the heart can be accessed with conventional open chest surgery. A positive electrode 14 and negative electrode 16 are applied externally to a portion of the infarcted portion 12 to induce resistive heating in the infarct scar in the desired treatment area 18 when energy is applied across the electrodes. Alternatively, the positive and negative electrodes can be inserted into the infarcted scar. The positive and negative electrodes function as a heating element as they are energized to raise the temperature of the scar in the desired treatment area 18 to a controlled temperature sufficient to reduce the surface area of the scar without ablating the scar tissue or damaging the healthy tissue surrounding the infarcted portion 12.
U.S. Pat. No. 6,071,303 also teaches other appliances for applying radiant energy or thermal energy, or to otherwise heat the infarcted tissue and reduce the area of the infarcted tissue. For example, as shown in FIG. 2 a radio-frequency generator 20 and heating element applicator 22 can be used. When the heating element 24 of the applicator 22 is positioned at the desired treatment site, the radio-frequency generator 20 is activated to provide suitable energy, preferably at a selected frequency in the range of 10 megahertz to 1000 megahertz, to heat the scar tissue to a temperature sufficient to reduce the surface area of the scar without ablating the scar tissue or damaging the healthy tissue surrounding the infarcted area 12.
It should be understood that the devices taught in U.S. Pat. No. 6,071,303 are located external to the heart. However, I have found that in certain circumstances it can be preferable to apply heat in the internal surface of the heart. For example, in some cases the scar tissue is more severe or larger or both, within the heart than on the surface. Also, the use of the devices taught in U.S. Pat. No. 6,071,303 can require conventional open chest surgery. However, in some cases it is desirable for the surgeon to gain access to the patient's heart by catheterization.
It is an object of the present invention to provide a means to apply heat to a patient's infarct scar using a device deployed by a catheterization procedure so that the device is located inside the heart.
It is another object of the present invention to provide a means to apply heat to a patient's infarct scar using a device located inside the heart to raise the temperature of the scar in the desired treatment area to a controlled temperature sufficient to reduce the surface area of the scar without ablating the scar tissue or damaging the healthy tissue surrounding the infarcted portion.
It is another object of the invention to provide a means to locate a patient's infarct scar.